1. Field of the Invention
The present invention relates to a coordinate input device and, more particularly, to a coordinate input device in which when a coordinate input object is brought into contact with an operation area to display a contact state of the operation area with a cursor, the cursor is suppressed from being finely moved in accordance with a moving speed of the coordinate input object.
2. Description of the Related Art
In recent years, a coordinate input device used by the following manner has developed. That is, when a coordinate input object such as an input pen or a finger is brought into contact with a desired position of a tablet-type operation area, coordinate data representing the coordinate positions of the contact portions are sequentially output to display the contact positions of the coordinate input object.
Here, FIG. 5 is a block diagram showing a known coordinate input device.
As shown in FIG. 5, the coordinate input device is constituted by a tablet 51, a coordinate input object 52 such as an input pen or a finger of an operator, a coordinate data generator 53, and a signal processor 54.
The tablet 51 is arranged to be perpendicular to the upper and lower surfaces of a substrate (not shown), and is constituted by a plurality of (N) electrodes 55 (X.sub.1 to X.sub.N) and a plurality of (M) electrodes 56 (Y.sub.1 to Y.sub.M) which are arranged in a matrix, a protective film (not shown) adhered to the upper surface of the substrate, and the like. The input pen 52 has a tip and a surface which consist of a conductive material. The coordinate data generator 53 is constituted by an X-axis side multiplexer 57, a Y-axis side multiplexer 58, a first amplification circuit 59, a first filter circuit 60, an analog/digital converter (A/D) 61, a controller (CPU) 62, an oscillation circuit 63, and an analog switch 64. In this case, the X-axis side multiplexer 57 has a plurality of (N) switches S.sub.1 to S.sub.N which are arranged in parallel to each other. One ends of the switches S.sub.1 to S.sub.N are connected to one ends of the X electrodes 55 (X.sub.1 to X.sub.N), respectively, and the other ends of the switches S.sub.1 to S.sub.N are connected to the analog switch 64 in common. The Y-axis side multiplexer 58 has a plurality of (M) switches S.sub.1 to S.sub.M which are arranged in parallel. One ends of the switches S.sub.1 to S.sub.M are connected to one ends of the Y electrodes 56 (Y.sub.1 to Y.sub.M), respectively, and the other ends of the switches S.sub.1 to S.sub.M are connected to the input terminal of the first amplification circuit 59 in common. One input terminal of the first filter circuit 60 is connected to the output terminal of the first amplification circuit 59, and the output terminal of the first filter circuit 60 is connected to the input terminal of the A/D 61. The CPU 62 has a data output terminal connected to the signal processor 54, and has a control terminal connected to the control terminal of the analog switch 64. The signal processor 54 is constituted by a known personal computer (PC) or the like, and comprises a liquid-crystal display unit 54a or a CRT display unit.
An operation of a known coordinate input device having the above arrangement will be briefly described below.
A case wherein the tablet 51 is operated with a finger 52 of an operator will be described. An oscillation signal from the oscillation circuit 63 is supplied to the X-axis side multiplexer 57. At this time, the switches S.sub.1 to S.sub.N of the X-axis side multiplexer 57 and the switches S.sub.1 to S.sub.M of the Y-axis side multiplexer 58 are ON/OFF-controlled with a control signal supplied from the CPU 62. The manner of this control is as follows. That is, the switch S.sub.1 of the X-axis side multiplexer 57 is turned on first, and the switches S.sub.1 to S.sub.M of the Y-axis side multiplexer 58 are sequentially turned on. The switch S.sub.2 of the X-axis side multiplexer 57 is turned on, the switches S.sub.1 to S.sub.M of the Y-axis side multiplexer 58 are sequentially turned on. Similarly, with respect to the switches S.sub.3 to S.sub.M of the X-axis side multiplexer 57, one of these switches is turned on, and the switches S.sub.1 to S.sub.M of the Y-axis side multiplexer 58 are sequentially turned on. With the above scanning operation, oscillation signals from the oscillation circuit 63 are sequentially supplied to the X electrodes 55 (X.sub.1 to X.sub.N), and the signal voltages of the oscillation signals generate electrostatic capacitors between the X electrodes 55 (X.sub.1 to X.sub.N) and the Y electrodes 56 (Y.sub.1 to Y.sub.M).
Here, when the finger 52 is brought into contact with a desired position on the tablet 51, some of electric lines of force generated by a capacitor near the contact position are absorbed by the finger 52, the capacitance of the electrostatic capacitor located at this portion, and the signal voltage extracted from the portion decreases according to a decrease in the capacitance. With the scanning operation of the X-axis side multiplexer 57 and the Y-axis side multiplexer 58, the signal voltages output from the Y electrodes 56 (Y.sub.1 to Y.sub.M) are amplified by the first amplification circuit 59 as in the case of detection at a Y-axis coordinate position by the operation of the input pen 52, and the signal voltages from which noise components are removed by the first filter circuit 60 are supplied to the A/D 61. The A/D 61 converts the input signal voltages into digital signals, and the CPU 62 loads the digital signals. The CPU 62 calculates the Y and X electrodes 56 and 55 each having the smallest signal voltage value on the basis of the loaded digital signals to detect a contact position of the finger 52 on the tablet 51.
In this manner, when detection for the X- and Y-coordinates of the position where the finger 52 touches on the tablet 51 is made, the CPU 62 sends the detection data to the signal processor 54. In the signal processor 54, the contact position of the finger 52 is displayed on the liquid-crystal display unit 54a by means of movement of the cursor, and selection or the like for a menu corresponding to the contact position of the finger 52 is performed.
When the tablet 51 is operated with the input pen 52, a generated electrostatic capacitance is absorbed by a hand holding the finger 52 through the input pen 52 to detect the X and Y coordinates of the finger 52 as described above.
In the known coordinate input device described above, assume that a coordinate input object such as the finger 52 of the operator is brought into contact with the tablet (operation area) 51 and that the contact position on the tablet 51 is moved. In this case, the moving speed of the coordinate input object on the tablet 51 generally varies, and the range of variation is of several Hz to 10 Hz as a frequency range. In addition, since the tablet 51 used in the known coordinate input device has often high sensitivity, a variation in the moving speed of the coordinate input object on the tablet 51 is detected. As a result, when the moving state of the coordinate input object on the tablet 51 is displayed on the display unit 54a of the signal processor 54, the cursor may finely move or vibrate disadvantageously.
In order to solve the above problem, in some of the known coordinate input devices, when coordinate data is output from the tablet 51, the CPU 62 performs a filter process to the coordinate data by using software, and a signal process is performed to remove fine movement or vibration of the cursor displayed on the liquid-crystal display unit 54a of the signal processor 54.
However, since a frequency component representing fine movement or vibration of the cursor may be approximate to a frequency component representing the moving speed of the coordinate input object on the tablet 51, when the CPU 62 performs a filter process by using software, the frequency component representing the moving speed of the coordinate input object on the tablet 51 is attenuated together with the frequency component representing the fine movement or vibration of the cursor. As a result, another problem that the movement of the cursor corresponding to the moving speed of the coordinate input object on the tablet 51 is delayed is posed.